A typical apparatus for continuously producing a metal strip comprises a mold including a pair of mold rolls opposed to each other with a clearance defining an outlet opening, and a melt receiver arranged above the rolls in contact therewith. Molten metal supplied into the mold is withdrawn under solidification through the outlet opening to produce a casting which is thereafter guided along a path provided by plural pairs of guide rolls.
As is well known, a casting (metal strip) produced by such an apparatus usually has on the opposite surfaces thereof depressions of about 0.1 mm in depth extending widthwise of the casting and spaced longitudinally at intervals of about 0.1 to 0.4 mm. These depressions, which are known as "tear marks" degrading the product value, are believed to be formed for the following reason. The molten metal in the mold continuously solidifies on the relatively cold rotating mold rolls to form a shell bifurcated from the upper end of the casting, whereas the melt also forms into a solidified shell on the interior surface of the melt receiver adjacent the mold rolls to ultimately merge into the bifurcated shell on the mold roll side. As the casting is continuously withdrawn at a constant speed, the thus merged shells are immediately torn apart, and they join together again after a certain interval. Such process repeatedly occurs at intervals to form a tear mark every time both shells are torn apart.
In case a casting has a large thickness, such tear marks can be eliminated by rolling the casting to provide an improved quality. But in the case of a thin casting, there is virtually no room for rolling to remove the tear marks, thus leading to a deteriorated product quality.